But Nasa said it remained hopeful that the mission would yield more interesting science, and said the rocky, windswept "Rocknest" site where it had gathered the samples was not the promising area to search.

"We have no definitive detection of Martian organics at this point, but we will keep looking in the diverse environments of Gale Crater," said Sample Analysis at Mars Principal Investigator Paul Mahaffy.

John Grotzinger, chief project scientist for the Curiosity mission - and the source of the "history books" quote - said that Nasa would be working hard to check if the organic compounds were from the Red Planet.

"Even though [Mahaffy's] instrument detected organic compounds, first of all we have to determine whether they're indigenous to Mars," he said.

Curiosity's SAM laboratory cooks Martian dirt in small ovens, before studying the gases that they give off. In this case it studied perchlorate, a compound of oxygen and chlorine that had been found in the Martian arctic previously by the Phoenix lander.

When it "cooked" the sample, it gave off both chlorinated methane and carbon. Finding carbon might indicate primitive life - because that is one of principal ways carbon is made on Earth. But Nasa remains unconvinced and said it would continue testing.

"We used almost every part of our science payload examining this drift," said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. "The synergies of the instruments and richness of the data sets give us great promise for using them at the mission's main science destination on Mount Sharp."